This invention relates to a printed wiring board provided with via-holes formed by using a laser beam and a method of manufacturing the same.
The printed wiring board is formed by laminating plural insulating layers 91xcx9c93 one upon the other and electrically connecting innerlayer conductor circuits 95, 97 arranged between the layers to an outer conductor circuit 94 existing on an outermost surface through metal plated films 96 formed on via-holes 99a, 99b as shown, for example, in FIG. 61. As the insulating layers 91xcx9c93 is used a resin substrate such as glass-epoxy substrate or the like. The via-holes 99a, 99b are blind via-holes each covered at its one end and opened at the other end.
As a method of forming the via-hole, there are a method using a drill, a method using a laser beam and the like.
However, the above drilling method causes unevenness in the depth accuracy. And also, it is recently demanded to make more fine a diameter of the via-hole with the advance of high densification in a wiring pattern.
For this end, there is proposed the formation of holes through the laser beam (JP-A-62-216297, JP-A-3-165594).
According to the latter method, as shown in FIG. 62, the via-holes 99a, 99b can be formed in a region ranging from an outermost surface of a multilayer laminated plate up to innerlayer conductor circuits existing therein by utilizing a property that laser beams 81 reflect on the innerlayer conductor circuits 95, 97 each made of a metal such as copper foil, metal plated film or the like.
In the printed wiring board, however, a relatively shallow via-hole 99a arrived at the innerlayer conductor circuit 95 near to the outermost surface of the printed wiring board and a relatively deep via-hole 99b arrived at the innerlayer conductor circuit 97 far away from the outermost surface are existent together as the via-hole as shown in FIG. 62.
As a result, when the holes are formed through the laser beam 81, as shown in FIG. 63, there may be caused damages 98 such as breakage, swell and the like in a central portion of the innerlayer conductor circuit 95 arranged in the bottom of the shallow via-hole 99b though the innerlayer conductor circuit 97 arranged in the bottom of the deep via-hole 99b is not damaged.
Once such damages are caused, when a metal plated film is formed on each surface of the innerlayer conductor circuit 95 and via-hole 99a and between such a surface and an outer conductor circuit, pieces 98a of the innerlayer conductor circuit broken due to the damage 98 remain in the via-hole 99a, so that the metal plated film may not be formed sufficiently. Such an insufficient metal plated film badly affects electric conduction between the innerlayer conductor circuit 95 and the outer conductor circuit 94 and sometimes rejects the printed wiring board itself.
The reason why the damage is caused in the innerlayer conductor circuit 95 as mentioned above is due to the fact that laser beams 81 having an intensity required for the formation of the deep via-hole 99b are irradiated to not only the shallow via-hole 99a but also the deep via-hole 99b as shown in FIG. 62.
Therefore, it is also considered to irradiate a laser beam having an intensity in accordance with the depth of the via-hole to be formed. However, the number of via-holes formed in one printed wiring board is as many as, for example, 500xcx9c10000, so that it is complicated to adjust the intensity of the laser beam every via-hole and also it is required to use an expensive control device for such an adjustment.
Furthermore, a black oxide film is formed on the surfaces of the innerlayer conductor circuits 95, 97 for ensuring an adhesion property to the insulating layers 91, 92. Since the black oxide film is high in the energy absorption of laser beam, there is a fear of causing damages such as breakage and the like due to fusion and swelling of the innerlayer conductor circuit provided on its surface with the black oxide film.
And also, the insulating layer made of the resin or the like is exposed in the via-hole, so that it is difficult to form the metal plated film. For this end, the joining property between he inner wall of the via-hole and the metal plated film is low and the peeling, dropping-out and the like of the metal plated film are caused, which have a fear of badly affecting the electric conduction of the via-hole.
The formation of the metal plated film on the via-hole is carried out by flowing an electric plating solution into the via-hole, but as the inner diameter of the hole becomes small, the flowing of the electric plating solution is difficult to make the formation of the plated film ununiform, so that there is caused a fear that the electric conduction of the via-hole is insufficient.
Further, it is attempted to provide the electric conduction by filling a solder in the via-hole instead of the metal plated film. In this case, the joining strength between the inner wall of the via-hole and the solder is low and there is a case that the solder is get out from the via-hole through an external pressure.
Moreover, it is required to utilize the irradiation of the laser beam to the formation of holes other than the via-hole.
In the light of the above problems, the invention is to provide a printed wiring board and a method of manufacturing the same which can form via-holes having a reliable electric conduction without causing damages of innerlayer conductor circuits through a laser beam and realize novel circuit formation through the laser beam.
A first aspect of the invention lies in a method of manufacturing a printed wiring board comprising at least two insulating layers made of a synthetic resin, an innerlayer conductor circuit arranged between the insulating layers, and a blind via-hole formed from an outermost surface of the insulating layer toward the innerlayer conductor circuit, characterized in that an opening hole is previously formed in a central portion of the innerlayer conductor circuit located in a bottom portion of the blind via-hole, and a laser beam is irradiated from the outermost surface of the insulating layer to form the blind via-hole, and then a metal plated film is formed on the innerlayer conductor circuit and the surface of the blind via-hole.
In the first aspect of the invention, it is most noticed that the opening hole is previously formed in the central portion of the innerlayer conductor circuit.
In the first aspect of the invention, the blind via-hole ranging from the outermost surface of the printed wiring board to the innerlayer conductor circuit is formed by irradiating the laser beam toward a portion forming the blind via-hole.
In this case, the insulating layer in the printed wiring board is vaporized and removed by a higher energy of the laser beam, whereby hole is gradually formed toward the inside of the printed wiring board. When the top of the laser beam arrives at the innerlayer conductor circuit, the laser beam is reflected by the innerlayer conductor circuit made of the metal. At this time, the irradiation of the laser beam is stopped. Thus, the formation of the blind via-hole is terminated.
It is important that the formation of many blind via-holes is carried out, for example, by successively and spottedly irradiating the laser beam every hole. On the other hand, the irradiation time and energy required for the formation of the hole differ between the shallow blind via-hole and the deep blind via-hole.
However, the irradiation is conducted successively and continuously as mentioned above, so that all holes are formed under the same condition every the hole by setting the time and energy so as to surely form the deep blind via-hole.
In the first aspect of the invention, the opening hole is formed in the innerlayer conductor circuit corresponding to the shallow blind via-hole.
In the formation of the shallow blind via-hole, therefore, even the laser beam already arrives at the innerlayer conductor circuit to complete the formation of the via-hole, the laser beam is successively irradiated under the condition forming the deep blind via-hole. In this case, however, a central portion of the laser beam having a large energy is irradiated to the opening hole to pass therethrough.
The laser beam passing through the opening hole is irradiated only to the insulating layer ahead the opening hole. Therefore, the insulating layer ahead the opening hole is somewhat pierced in the portion of the innerlayer circuit conductor, but the damage is not caused in the innerlayer conductor circuit itself.
On the other hand, the irradiation of the laser beam is stopped at a time of reflecting on the innerlayer conductor circuit in the formation of the deep blind via-hole, so that the damage is not caused.
And also, there is a method of simultaneously irradiating laser beams to all holes to be formed irrespectively of the shallow blind via-hole and deep blind via-hole. In this case, there are obtained the same function and effect as mentioned above (see the following embodiments).
With respect to the thus obtained blind via-holes having different depths, the metal plated film is formed in the inside of each hole in the same manner as in the conventional technique. In this case, all of the innerlayer conductor circuits do not cause the damage through the laser beam as mentioned above, so that a state of forming the insufficient metal plated film as described in the conventional technique can be avoided and the metal plated film having an excellent electric conduction can be formed.
As the insulating layer made of the synthetic resin in the first aspect of the invention, there are a synthetic resin alone, a resin substrate comprised of a synthetic resin and an inorganic filler, and a cloth substrate comprised of a synthetic resin and an inorganic cloth.
As the synthetic resin, mention may be made of epoxy resin, phenolic resin, polyimide resin, polybutadiene resin, fluoride resin and the like. The insulating layer made of only such a synthetic resin may be formed between another insulating layers as a prepreg adhesion layer as shown in the following embodiment.
As the inorganic filler added to the synthetic resin, mention may be made of glass short fibers, silica powder, mica powder, alumina, carbon and so on. The substrate made of a mixture of the synthetic resin and the inorganic filler is high in the strength as compared with the synthetic resin alone.
And also, the cloth substrate is a substrate comprised of a woven or knitted cloth and a synthetic resin such as glass-epoxy substrate, glass-polyimide substrate and so on. As such a cloth substrate, there is a substrate formed by impregnating the cloth with the synthetic resin. As a material of the cloth, there are glass fiber cloth, carbon cloth, aramide cloth and so on. As the synthetic resin, use may be made of the above materials.
The formation of the via-hole through the laser beam is carried out by irradiating the laser beam to a portion forming the blind via-hole. As the laser beam, it is preferable to use a carbon dioxide gas laser having a large energy and an excimer laser having no heat affection.
The blind via-hole is formed up to a given innerlayer conductor circuit arranged at the inside of the printed wiring board. In the thus formed blind via-hole, the metal plated film is continuously formed from the innerlayer conductor circuit at the bottom of the via-hole through a wall face of the via-hole to an outer conductor circuit.
When the innerlayer conductor circuit is provided on two or more stages in the printed wiring board and the blind via-hole is formed on each of the innerlayer conductor circuit, it is favorable to irradiate the laser beam at a state that the opening hole is formed in the innerlayer conductor circuit near to the outermost surface at a side of irradiating the laser beam, while the opening hole is not formed in the innerlayer conductor circuit far away from the outermost surface. Thus, there can be obtained the same function and effect as mentioned above.
The opening hole formed in the innerlayer conductor circuit is preferable to be 30-60% of a diameter of the blind via-hole. When the diameter of the opening hole is less than 30%, if a distance between the innerlayer conductor circuit having the opening hole and the deepest innerlayer conductor circuit having no opening hole is large, there is caused a fear that the innerlayer conductor circuit having the opening hole is damaged by the laser beam. On the other hand, when it exceeds 60%, there is caused a fear that the connection between copper plated film and the innerlayer conductor circuit is insufficient.
The metal plated film is favorable to be formed so as to cover the opening hole in the innerlayer conductor circuit. Thus, the bottom of the blind via-hole is completely covered with the metal plated film, so that there is caused no penetration of humidity into the blind via-hole.
Moreover, the first aspect of the invention is applicable to printed wiring boards requiring high connection reliability such as memory module, multi-chip module, mother board, daughter board, plastic package and the like.
A second aspect of the invention lies in a method of manufacturing a printed wiring board comprising at least two insulating layers made of a synthetic resin, an innerlayer conductor circuit arranged between the insulating layers, and a plurality of blind via-holes formed from an outermost surface toward the innerlayer conductor circuit and having different depths by successively irradiating a laser beam every a portion forming the blind via-hole, characterized in that a shallowest blind via-hole is formed as a standard hole by using a standard laser beam having an energy strength required for the formation of the standard hole, and the standard laser beam is irradiated plural times in the formation of the blind via-holes having deeper depths.
In the second aspect of the invention, it is most noticed that the standard hole is formed by irradiating the standard laser beam, while the blind via-holes having a depth deeper than the standard hole are formed by irradiating the standard laser beam plural times.
The function and effect of the second aspect of the invention will be described below.
In the second aspect of the invention, the blind via-hole ranging from the outermost surface of the printed wiring board to the innerlayer conductor circuit is formed by irradiating the laser beam toward a portion forming the blind via-hole.
In this case, the insulating layer in the printed wiring board is vaporized and removed by a higher energy of the laser beam, whereby hole is gradually formed toward the inside of the printed wiring board. When the top of the laser beam arrives at the innerlayer conductor circuit, the laser beam is reflected by the innerlayer conductor circuit made of the metal. At this time, the irradiation of the laser beam is stopped. Thus, the formation of the blind via-hole is terminated.
And also, the formation of many blind via-holes is carried out, for example, by successively and spottedly irradiating the laser beam every hole. In this case, the irradiation time and energy required for the formation of the hole differ between the shallow blind via-hole and the deep blind via-hole.
In the second aspect of the invention, therefore, the standard laser beam having an energy strength required for the formation of a shallowest blind via-hole as a standard hole is used and the formation of the standard hole is conducted by irradiating the standard laser beam at a time. On the other hand, the blind via-holes having a depth deeper than the standard hole are formed by irradiating the standard laser beam plural times.
According to the second aspect of the invention, therefore, many blind via-holes are divided into the standard holes and the other blind via-holes, and the irradiation number of the standard laser beam may be determined in accordance therewith. And also, the blind via-holes other than the standard hole have several kinds of depths. The depth of each blind via-hole can previously be known in the planning of the printed wiring board.
On the other hand, an oscillator for the laser beam irradiates the standard laser beam every a case that the oscillator is moved to a coordinate point indicating, for example, a position of each blind via-hole. And also, the movement and stop to the coordinate point are carried out by N/C control by means of a coordinate control device for the positioning.
When the irradiation number of the standard laser beam required every the blind via-hole is set, for example, in the laser beam oscillator positioned by the coordinate control device, therefore, the energy strength required every the blind via-hole can be irradiated.
As a result, the time required for the formation of many blind via-holes is shortened and the cost can be reduced. And also, it is enough to control whether or not the irradiation is required plural times, so that the cost of the device can be reduced.
According to the second aspect of the invention, therefore, many blind via-holes having different depths can easily be formed only by adjusting the irradiation number of the standard laser beam.
Moreover, the depth of the blind via-hole is a depth ranging from the outermost surface of the printed wiring board to the innerlayer conductor circuit (including a lower circuit at a bottom surface), and each depth differs in accordance with a distance between the innerlayer conductor circuits. And also, the distance is determined by a thickness of the insulating layer between the innerlayer conductor circuits. Therefore, the depth of the blind via-hole other than the standard hole becomes generally near to an integer times a depth of the standard hole. As a result, the blind via-holes other than the standard hole can be formed by irradiating the standard laser beam plural times.
As the insulating layer made of the synthetic resin in the second aspect of the invention, there are a synthetic resin alone, a resin substrate comprised of a synthetic resin and an inorganic filler, and a cloth substrate comprised of a synthetic resin and an inorganic cloth.
As the synthetic resin, mention may be made of epoxy resin, phenolic resin, polyimide resin, polybutadiene resin, fluoride resin and the like. The insulating layer made of only such a synthetic resin may be formed between another insulating layers as a prepreg adhesion layer.
As the laser beam, it is preferable to use a carbon dioxide gas laser having a large energy and an excimer laser having no heat affection.
For example, the energy strength of the standard laser beam can experimentally be determined by frequency, power (W) and irradiation time of the laser beam.
Moreover, the blind via-hole is formed up to a given innerlayer conductor circuit. In the thus formed blind via-hole, a metal plated film is continuously formed from the innerlayer conductor circuit at the bottom of the via-hole through the inner wall of the via-hole to an outer conductor circuit (see FIG. 10).
Furthermore, it is favorable that the standard laser beam is irradiated one time to the formation of all blind via-holes and thereafter the standard laser beam is irradiated only to the blind via-holes having a depth deeper than the standard hole at irradiation number required for the formation of these via-holes.
In this way, there can be obtained an effect of forming holes having various depths at a uniform state in the same cycle.
The standard laser beam is irradiated so as to successively form adjacent blind via-holes. In this case, it is favorable that one irradiation is conducted in the formation of the standard hole and the irradiation for the formation of the blind via-holes having a depth deeper than the standard hole is conducted at number required for such a via-hole each time.
Thus, movement not requiring for the formation such as movement of a table or the like can be controlled to a minimum level, so that a total formation time can be shortened.
Moreover, the second aspect of the invention is applicable to printed wiring boards requiring high connection reliability such as memory module, multi-chip module, mother board, daughter board, plastic package and the like.
A third aspect of the invention lies in a method of manufacturing a printed wiring board by forming an innerlayer conductor circuit on a surface of an innerlayer substrate, forming a black oxide film on a surface of the innerlayer conductor circuit, forming a second conductor circuit onto the innerlayer substrate through an insulating layer, irradiating a laser beam to form a via-hole ranging from an outer most surface of the insulating layer to the innerlayer conductor circuit, and then forming a metal plated film onto an inner wall face of the via-hole, characterized in that a portion of the innerlayer conductor circuit irradiated by the laser beam is an exposed portion having no black oxide film.
The formation of hole through the laser beam is carried out by irradiating the laser beam to a portion forming the via-hole. As the laser beam, it is favorable to use a carbon dioxide gas laser having a large energy and an excimer laser having no heat affection.
And also, the formation of the via-hole through the laser beam is conducted by vaporizing and removing the insulating layer by a higher energy of the laser beam to successively form a hole toward the inside of the printed wiring board. When the top of the laser beam arrives at the innerlayer conductor circuit, the laser beam is reflected by the innerlayer conductor circuit made of the metal. At this time, the irradiation of the laser beam is stopped.
The function of the third aspect of the invention will be described.
In the method according to the third aspect of the invention, the portion irradiated by the laser beam is an exposed portion of the innerlayer conductor circuit having no black oxide film.
Therefore, the laser beam is reflected by the innerlayer conductor circuit made of the metal and hardly absorbed by the innerlayer conductor circuit. As a result, it can be prevented to abnormally heat the innerlayer conductor circuit, so that there is not caused the damage of the innerlayer conductor circuit through heat.
In the third aspect of the invention, therefore, the via-hole can be formed by using the laser beam without damaging the innerlayer conductor circuit. And also, the via-hole is formed by the laser beam, so that via-holes having a smaller diameter can be obtained and it is easy to manufacture a printed wiring board having high density and accuracy.
As mentioned above, according to the third aspect of the invention, there can be provided a method of manufacturing a multilayer printed wiring board without causing the damage of the innerlayer conductor circuit in the formation of the via-hole through the laser beam.
Furthermore, the printed wiring board obtained in the third aspect of the invention can be used in memory module, multi-chip module, mother board, daughter board, plastic package and the like which require a high connection reliability.
The exposed portion is preferable to be formed by forming the black oxide film on the innerlayer conductor circuit and thereafter etching the black oxide film. Thus, the black oxide film can easily be formed at arbitrary positions.
Alternatively, the exposed portion is preferable to be formed by partly masking the innerlayer conductor circuit so as not to form the black oxide film in the formation of the black oxide film on the innerlayer conductor circuit.
In this way, the exposed portion can easily be formed in the formation of the black oxide film.
The insulating layer and the second conductor circuit are favorable to be formed at two or more sets. Thus, there can easily be obtained a printed wiring board of high density wiring.
Moreover, when the insulating layer and the second conductor circuit are two or more sets, a set of certain insulating layer and second conductor circuit formed thereon is provided on its surface with another set of different insulating layer and second conductor circuit formed thereon (see FIG. 20). That is, the second conductor circuit is formed on the insulating layer, so that they are used as one set for the formation of the multi-layer.
In this case, a via-hole ranging from an outermost surface of an outermost insulating layer to a surface of either second conductor circuit may be formed (see FIG. 20).
Furthermore, it is favorable that the black oxide film is also formed on the surface of the second conductor circuit likewise the innerlayer conductor circuit and the portion irradiated by the laser beam for the formation of the via-hole is an exposed portion having no black oxide film (see the following embodiment 3).
Moreover, the printed wiring board obtained by the above method is, for example, a printed wiring board comprising an insulating layer, an innerlayer conductor circuit arranged adjacent to the insulating layer and provided on its surface with a black oxide film and a via-hole extending from an outermost surface of the insulating layer to the innerlayer conductor circuit, characterized in that an exposed portion having no black oxide film is formed on the innerlayer conductor circuit in a position corresponding to the bottom of the via-hole.
In such a printed wiring board, the black oxide film is not existent on the portion of the innerlayer conductor circuit corresponding to the bottom of the via-hole, so that the innerlayer conductor circuit is exposed at this portion. The laser beam is hardly absorbed on this portion.
Therefore, when the laser beam is irradiated to the insulating layer for forming the via-hole in the insulating layer, it can be prevented to abnormally heat the innerlayer conductor circuit and also it can be prevented to cause the damage due to fusion of the innerlayer conductor circuit or the like.
As mentioned above, according to the third aspect of the invention, there can be provided the multilayer printed wiring board causing no damage in the innerlayer conductor circuit in the formation of the via-hole through the laser beam.
A fourth aspect of the invention lies in a printed wiring board comprising two or more insulating layers located on an innerlayer conductor circuit, a via-hole extending from an outermost surface of the insulating layer through the two or more insulating layers to the innerlayer conductor circuit, and an inner metal plated film formed in the via-hole and electrically connecting the innerlayer conductor circuit to an outer conductor circuit formed on the outermost surface, characterized in that an annular middle land having an opening hole is arranged so as to protrude into the inside of the via-hole, and the via-hole is a stepped via-hole consisting of an outer via-hole segment located outside the annular middle land and an inner via-hole segment located at the side of the innerlayer conductor circuit and having a diameter smaller than that of the outer via-hole segment and a stepped portion located at the annular middle land, and the inner metal plated film is a stepped plated film formed along inner wall faces of the outer via-hole segment and the inner via-hole segment.
The function of the fourth aspect of the invention will be described below.
In the printed wiring board according to the fourth aspect of the invention is arranged the annular middle land having an opening hole so as to protrude into the inside of the via-hole. And also, the via-hole is a stepped via-hole having a stepped portion on the annular middle land. Furthermore, the inner metal plated film is a stepped plated film formed along the inner wall faces of the outer via-hole segment and the inner via-hole segment.
The annular middle land is exposed in the stepped portion of the via-hole. Such an exposed portion is a ring having an outer diameter equal to the diameter of the outer via-hole segment and an inner diameter equal to the diameter of the inner via-hole segment. This portion contacts with the inner metal plated film forming the stepped plated film (see FIG. 27).
The inner metal plated film hardly joins to the exposed portion of the insulating layer in the via-hole, but can strongly join to the annular middle land. Therefore, the inner metal plated film is joined to the exposed portion of the annular middle land, whereby it can strongly be joined to the inside of the via-hole.
And also, the side face of the opening hole in the annular middle land is exposed to the via-hole, so that the inner metal plated film can also be joined to this portion.
Therefore, the peeling and dropping of the inner metal plated film can be prevented.
Now, a boundary conductor circuit as mentioned later may be arranged in a boundary portion. However, when the via-hole is formed in a portion having no boundary conductor circuit, a thickness of an opening peripheral edge of the via-hole becomes thinner by a thickness of the boundary conductor circuit as compared with a place having the boundary conductor circuit arranged in the boundary portion. As a result, a depression corresponding to the thickness of the boundary conductor circuit is formed in the opening peripheral edge of the via-hole.
When the annular middle land is arranged, the thickness of the annular middle land thickens the thickness of the opening peripheral edge of the via-hole, so that the occurrence of the depression in the opening peripheral edge of the via-hole can be prevented.
As mentioned above, according to the fourth aspect of the invention, there can be provided the printed wiring board wherein the inner metal plated film is strongly joined to the inside of the via-hole.
It is favorable that the annular middle land is a dummy land not connected to the boundary conductor circuit arranged in the boundary portion facing tow or more insulating layers to each other.
Thus, when many insulating layers are laminated, even if via-holes are formed portions of these insulating layers having no boundary conductor circuit, the occurrence of the depression in the opening peripheral edge of the via-hole can be prevented.
It is favorable that the annular middle land is an electrically conductive land connecting to the boundary conductor circuit arranged in the boundary portion facing two or more insulating layers to each other.
In this case, three or more conductor layers can be connected to each other through one via-hole. Therefore, the wiring area of the via-hole and land is reduced, so that it is possible to make a high densification.
The annular middle land is preferable to be made of a metal such as copper, nickel or the like.
As the method of manufacturing the above printed wiring board, there is, for example, a method of manufacturing a printed wiring board by arranging two or more insulating layers on an innerlayer conductor circuit, forming a via-hole so as to extend from an outermost surface of the insulating layer through the two or more insulating layers to the innerlayer conductor circuit, forming an inner metal plated film in the via-hole to electrically conduct the innerlayer conductor circuit to an outer conductor circuit arranged on the outermost surface, arranging an annular middle land having an opening hole so as to protrude into the inside of the via-hole, wherein the via-hole is a stepped via-hole consisting of an outer via-hole segment located outside the annular middle land and an inner via-hole segment located at the side of the innerlayer conductor circuit and having a diameter smaller than that of the outer via-hole segment and a stepped portion located at the annular middle land, and the inner metal plated film is a stepped plated film formed along inner wall faces of the outer via-hole segment and the inner via-hole segment, characterized in that the via-hole is formed by irradiating a laser beam from the outermost surface toward the innerlayer conductor circuit in which the laser beam is arrived to the innerlayer conductor circuit through the opening hole of the annular middle land and irradiated to a range required for forming the diameter of the outer via-hole segment, and the metal plated film is formed after the formation of the via-hole.
According to this manufacturing method, the printed wiring board wherein the inner metal plated film is strongly joined to the inside of the via-hole can be provided likewise the fourth aspect of the invention.
Since the via-hole is formed by the irradiation of the laser beam, via-holes having a very fine diameter of not more than 300 xcexcm can easily be obtained.
As mentioned above, according to this method, there can easily be manufactured a printed wiring board having fine-diameter via-holes in which the inner metal plated film is strongly joined to the inside of the via-hole.
The formation of the via-hole through the laser beam is carried out by irradiating the laser beam to a portion forming the via-hole. As the laser beam, it is favorable to use a carbon dioxide gas laser having a large energy and an excimer laser having no heat affection.
And also, in the formation of the via-hole by the irradiation of the laser beam, the insulating layers are vaporized and removed by a high energy to successively form a hole toward the inside of the printed wiring board.
In this case, the laser beam forming the neighborhood of the outer diameter of the via-hole is reflected on the annular middle land. Therefore, the insulating layer existing beneath the annular middle land remains as it is.
Furthermore, the laser beam forming a central portion of the via-hole passes through the opening hole of the annular middle land to vaporize and remove a further lower insulating layer. Thereafter, when the laser beam arrives at the innerlayer conductor circuit, it is reflected by the innerlayer conductor circuit made of the metal. Therefore, the irradiation of the laser beam stops at this time.
Thus, the via-hole formed by the laser beam is large in the outer diameter at a position above the annular middle land and small in the outer diameter located beneath the annular middle land.
That is, the stepped via-hole having a stepped portion can be formed.
The annular middle land is preferable to be a dummy land not connecting to the boundary conductor circuit arranged in the boundary portion facing the two or more insulating layers to each other.
The annular middle land is preferable to be an electrically conductive land connecting to the boundary conductor circuit arranged in the boundary portion facing the two or more insulating layers to each other.
In any case, the same function and effect as mentioned above can be obtained.
A fifth aspect of the invention lies in a printed wiring board comprising two or more insulating layers on an innerlayer conductor circuit, a via-hole extending from an outermost surface of the insulating layer through the two or more insulating layers to the innerlayer conductor circuit and an inner metal plated film formed in the via-hole so as to electrically connect the innerlayer conductor circuit to an outer conductor circuit arranged on the outermost surface, characterized in that an annular dummy land for reinforcement having an opening hole around the via-hole is arranged in a boundary portion facing the two or more insulating layers to each other and is joined to the inner metal plated film.
In the printed wiring board, an innerlayer conductor circuit may be arranged in the boundary portion, but the annular dummy land is separately arranged so as not to connect to such an innerlayer conductor circuit and is a reinforcing land. The annular dummy land is favorable to be made of a metal such as copper nickel or the like.
The function of the fifth aspect of the invention will be described below.
In the printed wiring board according to the fifth aspect of the invention, the annular reinforcing dummy land is arranged around the via-hole and is joined to the inner metal plated film in the via-hole.
The inner metal plated film hardly joins to an exposed portion of the insulating layer in the via-hole, but strongly joins to the side face of the annular dummy land. Therefore, the inner metal plated film is strongly joined to the inside of the via-hole.
As a result, the peeling and dropping-out of the inner metal plated film can be prevented.
Now, the innerlayer conductor circuit may be arranged in the boundary portion, but when the via-hole is formed in a portion having no innerlayer conductor circuit, an opening peripheral edge of the via-hole becomes thin by a thickness of the innerlayer conductor circuit as compared with a place having the innerlayer conductor circuit in the boundary portion. For this end, a depression corresponding to the thickness of the innerlayer conductor circuit is formed in the opening peripheral edge of the via-hole. This is particularly liable to be caused in the via-hole formed by passing through four or more insulating layers (see FIG. 33). The occurrence of the depression in the opening peripheral edge of the via-hole can be prevented by arranging the annular dummy land.
As mentioned above, according to the fifth aspect of the invention, there can be provided the printed wiring board in which the inner metal plated film is strongly joined to the inside of the via-hole.
And also, the printed wiring board obtained in the fifth aspect of the invention can be used in, for example, memory module, multi-chip module, mother board, daughter board, plastic package or the like which highly requires the connection reliability.
The annular dummy land is favorable to have an outer diameter larger than the diameter of the via-hole and include an opening hole having a diameter equal to the diameter of the via-hole.
Thus, the annular dummy land can more stably be arranged and also the reinforcing effect can be more enhanced.
As the method of manufacturing the above printed wiring board, there is a method of manufacturing a printed wiring board comprising two or more insulating layers on an innerlayer conductor circuit, a via-hole extending from an outermost surface of the insulating layer through the two or more insulating layers to the innerlayer conductor circuit and an inner metal plated film formed in the via-hole so as to electrically connect the innerlayer conductor circuit to an outer conductor circuit arranged on the outermost surface, wherein an annular dummy land for reinforcement having an opening hole around the via-hole is arranged in a boundary portion facing the two or more insulating layers to each other and is joined to the inner metal plated film, characterized in that the via-hole is formed by irradiating a laser beam from the outermost surface toward the innerlayer conductor circuit in which the laser beam is arrived to the innerlayer conductor circuit through the opening hole of the annular dummy land, and thereafter the inner metal plated film is formed.
According to this method, a printed wiring board wherein the inner metal plated film is strongly joined to the inside of the via-hole can be obtained likewise the above printed wiring board.
Since the via-hole is formed by the irradiation of the laser beam, via-holes having a very fine diameter of not more than 300 xcexcm can easily be obtained.
As mentioned above, according to this method, there can easily be manufactured a printed wiring board having fine-diameter via-holes in which the inner metal plated film is strongly joined to the inside of the via-hole.
The formation of the via-hole through the laser beam is carried out by irradiating the laser beam to a portion forming the via-hole. As the laser beam, it is favorable to use a carbon dioxide gas laser having a large energy and an excimer laser having no heat affection.
And also, in the formation of the via-hole by the irradiation of the laser beam, the insulating layers are vaporized and removed by a high energy to successively form a hole toward the inside of the printed wiring board. When the laser beam arrives at the innerlayer conductor circuit, it is reflected by the innerlayer conductor circuit made of the metal. Therefore, the irradiation of the laser beam stops at this time.
The annular dummy land is favorable to have an outer diameter larger than the diameter of the via-hole and include an opening hole having a diameter equal to the diameter of the via-hole.
Thus, the annular dummy land can more stably be arranged and also the reinforcing effect can be more enhanced likewise the above case.
A sixth aspect of the invention lies in a printed wiring board comprising an insulating layer, an upper conductor circuit arranged on an upper surface of the insulating layer, a lower conductor circuit arranged on a lower surface thereof, a blind via-hole passing through the insulating layer between the upper conductor circuit and the lower conductor circuit and bottomed at the lower conductor circuit and a via-plated layer formed on an inner wall face of the blind via-hole so as to electrically connect the upper conductor circuit to the lower conductor circuit, characterized in that a flowing hole of a plating solution having a diameter smaller than the blind via-hole is formed in the lower conductor circuit constituting the bottom of the blind via-hole.
The diameter of the flowing hole of the plating solution differs in accordance with the diameter of the blind via-hole, but when the diameter of the blind via-hole is 0.1xcx9c0.3 mm, the diameter of the flowing hole of the plating solution is preferable to be 0.0xcx9c10.1 mm.
Thus, the uniform via-plated layer can be obtained.
Moreover, when the diameter of the flowing hole is less than 0.01 mm, it is feared that the object of flowing the plating solution can not be attained. While, when it exceeds 0.1 mm, the hole is not closed with the plated film and it is feared to cause a problem that a leakage of a solder is created in the filling of the solder.
The function of the sixth aspect of the invention will be described below.
In the printed wiring board according to the sixth aspect of the invention, the flowing hole of the plating solution having a diameter smaller than the blind via-hole is formed in the lower conductor circuit constituting the bottom of the blind via-hole.
In the formation of the via-plated layer, the plating solution can be flowed through the flowing hole into inside and outside of the blind via-hole. For this end, the plating solution sufficiently containing a plating component always contacts with the inner wall face of the blind via-hole, so that the uniform via-plated layer can be obtained without causing a spotted state.
Therefore, there can be obtained the printed wiring board having an excellent electric conduction between the upper conductor circuit and the lower conductor circuit or an excellent connection reliability therebetween.
As mentioned above, according to the sixth aspect of the invention, there can be provided a printed wiring board wherein the via-plated layer is uniformly formed on the blind via-hole without causing the spotted state.
The printed wiring board obtained in the sixth aspect of the invention can be used in, for example, memory module, multi-chip module, mother board, daughter board, plastic package or the like which highly requires the connection reliability.
Of course, the sixth aspect of the invention is applicable to not only the printed wiring board having a single insulating layer but also the printed wiring board having plural insulating layers.
It is preferable that the flowing hole of plating solution is closed with the via-plated layer. Thus, a quantity of the solder can be uniformed in the filling of the solder.
It is favorable that the diameter of the flowing hole of plating solution is 10xcx9c40% of the diameter of the blind via-hole. Thus, the flowing of the plating solution can sufficiently be carried out. On the other hand, when the diameter of the flowing hole is less than 10% of the diameter of the blind via-hole, there is a fear that the object of flowing the plating solution can not be attained. While, when it is more than 40%, there is a fear that the closing of the hole by plating is insufficient.
As the method of manufacturing the above printed wiring board, there is a method of manufacturing a printed wiring board comprising an insulating layer, an upper conductor circuit arranged on an upper surface of the insulating layer, a lower conductor circuit arranged on a lower surface thereof, a blind via-hole passing through the insulating layer between the upper conductor circuit and the lower conductor circuit and bottomed at the lower conductor circuit and a via-plated layer formed on an inner wall face of the blind via-hole so as to electrically connect the upper conductor circuit to the lower conductor circuit, wherein a flowing hole of a plating solution having a diameter smaller than the blind via-hole is formed in the lower conductor circuit constituting the bottom of the blind via-hole, characterized in that the blind via-hole is formed by irradiating a laser beam from the upper surface of the insulating layer toward the lower conductor circuit, and the flowing hole of the plating solution is formed in the lower conductor circuit through the laser beam in the formation of the blind via-hole, and a chemical plating solution is flowed in the blind via-hole and the flowing hole of the plating solution to form a chemical plated layer in the blind via-hole, and thereafter an electroplating is carried out by flowing an electroplating solution to form the via-plated layer.
In this manufacturing method, the electroplating is carried out by utilizing the flowing hole of the plating solution formed in the lower conductor circuit and flowing the electroplating solution to form the via-plated layer. In this case, the electroplating solution can sufficiently be come and gone to the outside and inside of the blind via-hole through the flowing hole of the plating solution. Thus, the uniform via-plated layer can be obtained without causing the spotted state.
Since the via-hole is formed by the laser beam, via-holes having a smaller diameter can be obtained, so that t is easy to manufacture a printed wiring board having high density and accuracy.
Moreover, the formation of via-hole through the maser beam is carried out by irradiating the laser beam to a portion forming the via-hole. As the laser beam, it is favorable to use a carbon dioxide gas laser having a large energy and an excimer laser having no heat affection.
In the formation of the via-hole by the irradiation of the laser beam, the insulating layer is vaporized and removed by a high energy to successively form the via-hole toward the inside of the printed wiring board. When the top of the laser beam arrives at the lower conductor circuit, it is reflected on the lower conductor circuit made of a metal. Therefore, the irradiation of the laser beam stops at this time.
And also, the energy of the laser beam is high in the central portion and low in the peripheral edge portion. Therefore, the flowing hole of the plating solution can easily be formed in the central portion of the lower conductor circuit constituting the bottom of the blind via-hole by using the laser beam.
It is favorable that an exposed portion of the insulating layer for the formation of the flowing hole of the plating solution (i.e. a portion having no innerlayer conductor circuit) is previously formed in the innerlayer conductor circuit. The laser beam is reflected because the lower conductor circuit is made of a metal such as copper foil or the like. By forming the exposed portion, the insulating layer located above the exposed portion is vaporized and removed, whereby the flowing hole of the plating solution can be obtained.
A seventh aspect of the invention lies in a method of manufacturing a printed wiring board comprising a step of forming an upper pattern on an upper surface of an insulating substrate in a peripheral edge of a portion for the formation of an electric conduction hole, a step of forming a lower pattern closing the portion for the formation of the electric conduction hole on a lower surface of the insulating substrate, a step of forming the electric conduction hole in the insulating substrate, and a step of a metal plated film on an inner wall face of the electric conduction hole by a chemical plating treatment and an electroplating treatment, characterized in that the electroplating treatment is carried out by applying a current having a current density of 0.8xcx9c1.4 A/dm2 to a chemical plated film covering the inner wall face of the electric conduction hole at a state of immersing the insulating substrate in an electroplating bath.
The function and effect of the seventh aspect of the invention will be described below.
In the seventh aspect of the invention, the current density of the current applied to the chemical plated film is made smaller than that of the conventional technique as mentioned above. For this end, a thick plated film can be formed in the inner wall face of the electric conduction hole. Therefore, the mechanical strength of the metal plated film becomes high and the electric connection reliability of the electric conduction hole is improved.
And also, the metal plated film having a sufficient thickness can be formed even on the inner wall face of the electric conduction hole having a smaller diameter, so that the high density packaging of the electric conduction hole can be realized.
Moreover, the step of forming the upper pattern, the step of forming the lower pattern and the step of forming the electric conduction hole may be conducted either way and are not in order.
The metal plated film is preferable to be copper. In this case, the metal plated film having a good ductility and a small electric resistance can be formed.
The electroplating treatment is favorable to be carried out two or more times. Thus, the metal plated film having a thicker thickness can be formed in a short time. And also, the thickness of the metal plated film can be uniformed. On the other hand, when the electroplating treatment is conducted only one time, there is a case that a long time is taken in the formation of the thick metal plated film.
The upper pattern and lower pattern mean any electric conducting patterns formable on the surface of the insulating substrate such as wiring circuit, pad, terminal, land and the like, which may be formed, for example, by etching of a metal foil, a metal plating or the like.
As the insulating substrate, there are synthetic resin alone, prepreg and the like. As the synthetic resin, there are epoxy resin, phenolic resin, polyimide resin, polybutadiene resin, fluorine resin and so on.
The printed wiring board is composed of a single insulating substrate or of a laminate of two or more insulating substrates. In case of the laminate of two or more insulating substrates, the electric conduction hole may pass through all insulating substrates or may pass through a part of the insulating substrates.
The above printed wiring board can be used in, for example, memory module, multi-chip module, mother board, daughter board, plastic package or the like.
As the formation of the electric conduction hole, there are, for example, a method of irradiating a laser beam to a hole forming portion of the insulating layer, a method of chemically melting a hole forming portion of the insulating layer and the like.
An eighth aspect of the invention lies in a printed wiring board comprising an insulating substrate, a conductor pattern formed on a surface of the insulating substrate, a solder filling hole passing through the insulating substrate and arriving at an upper surface of the conductor pattern and a solder filled in the solder filling hole, characterized in that the insulating substrate includes fibers therein, and end portions of the fibers protrude from a wall face of the solder filling hole and encroach into the solder.
The function and effect of the eighth aspect of the invention will be described below.
In the eighth aspect of the invention, the end portions of the fibers included in the insulating substrate protrude from the wall face of the solder filling hole. These end portions of the fibers encroach into the solder filled in the solder filling hole. Therefore, the solder is strongly bonded to the solder filling hole. As a result, even when the printed wiring board is subjected to dynamic action from exterior, the solder never gets out of the solder filling hole.
Since the end portions of the fibers protruded from the wall face of the solder filling hole encroach into the solder, even when the insulating substrate is a thin sheet of about 0.05xcx9c0.20 mm and a bonding area between the solder and the solder filling hole is small, the solder never gets out of the solder filling hole. In the protrusion of the end portions of the fibers from the wall face of the solder filling hole, there is, for example, a method of conducting the formation of the solder filling hole through a laser beam.
The fiber is preferable to be one or more of glass fiber, resin fiber and ceramic fiber. Thus, the encroaching force of the fiber into the inside of the solder is increased and the bonding strength between the solder and the solder filling hole is more increased.
The fibers are included in the insulating substrate at a state of, for example, felt or cloth.
As the method of producing the above printed wiring board, there is a method of a printed wiring board by filling a solder into an inside of a solder filling hole, characterized in that a conductor pattern is first formed on a surface of an insulating substrate including fibers, and then a laser beam is irradiated to a portion of the insulating substrate not covered with the conductor pattern toward the conductor pattern to form a solder filling hole at a state of protruding end portions of the fibers included in the inside of the insulating substrate from a wall face of the solder filling hole, and thereafter a solder is filled into the inside of the solder filling hole.
In the method of the eighth aspect, the solder filling hole is formed by the irradiation of the laser beam, whereby the end portions of the fibers are left in the wall face of the solder filling hole. Therefore, the end portions of the fibers can easily be protruded from the wall face of the solder filling hole.
And also, the laser beam can form the solder filling hole in only the insulating substrate, in which the conductor pattern covering an opening portion of the solder filling hole can be left as it is. For this end, the production step can be simplified by forming conductor patterns on front and back surfaces of the insulating substrate before the formation of the solder filling hole.
The fiber is preferable to be one or more of glass fiber, resin fiber and ceramic fiber. Thus, the encroaching force of the fiber into the inside of the solder is increased and the bonding strength between the solder and the solder filling hole is more increased.
The fibers are included in the insulating substrate at a state of, for example, felt or cloth.
A ninth aspect of the invention lies in a printed wiring board comprising at least two insulating layers, an innerlayer conductor circuit between the insulating layers, a blind via-hole formed from an outermost surface toward the innerlayer conductor circuit, and a solder filled in the inside of the blind via-hole, characterized in that the blind via-hole has an uneven form at a section of its wall face.
The function of the ninth aspect of the invention will be described below.
In the printed wiring board according to the ninth aspect of the invention, the wall face of the blind via-hole has a section of uneven form.
Therefore, the solder filled in the blind via-hole comes into the unevenness and is fixed thereto. As a result, the solder can provide a high bonding strength to the blind via-hole.
The printed wiring board obtained in the ninth aspect of the invention can be used in, for example, memory module, multi-chip module, mother board, daughter board, plastic package or the like which highly requires the connection reliability.
As the above uneven form, there are preferably a concave form widening in a lateral direction of the blind via-hole, a convex form protruding inward in the blind via-hole, and a wavy form (see FIG. 52, FIG. 54, FIG. 55 as mentioned later).
In this way, the filled solder can surely be bonded to the inside of the blind via-hole.
It is favorable that the solder filled in the blind via-hole is connected to another PC board through a solder ball.
Thus, the electric conduction between the PC board and the blind via-hole can surely be held.
Moreover, the PC board includes various boards provided with printed circuits. Concretely, there are mentioned mother board, daughter board, memory module, multi-chip module, card module and the like for various apparatuses.
As the method of producing the above printed wiring board, there is a method of producing a printed wiring board, which comprises at least two insulating layers, an innerlayer conductor circuit between the insulating layers, a blind via-hole formed from an outermost surface toward the innerlayer conductor circuit and having an uneven form at a section of its wall face, and a solder filled in the inside of the blind via-hole, characterized in that the blind via-hole is formed by irradiating a laser beam, and thereafter molten solder is flowed into the blind via-hole.
According to the above method, there can be produced the printed wiring board in which the section of the wall face of the blind via-hole is uneven form.
Therefore, the solder filled in the blind via-hole can come into the unevenness. As a result, the solder can provide a high bonding strength to the blind via-hole.
And also, the blind via-hole is formed by the irradiation of the laser beam, so that a very fine size of not more than 300 xcexcm can be obtained.
The formation of the blind via-hole through the laser beam is carried out by irradiating laser beam to a portion forming the blind via-hole. As the laser beam, it is favorable to use a carbon dioxide gas laser having a large energy and an excimer laser having no heat affection.
In the formation of the blind via-hole by the irradiation of the laser beam, the insulating layer is vaporized and removed by a high energy to successively form the via-hole toward the inside of the printed wiring board. When the top of the laser beam arrives at the innerlayer conductor circuit, the laser beam is reflected on the innerlayer conductor circuit made of a metal. Therefore, the irradiation of the laser beam stops at this time.
Moreover, it is favorable that the insulating substrate is comprised of a prepreg obtained by impregnating a resin into a substrate of glass cloth or the like because the blind via-hole having a section of irregular form can be obtained only by the irradiation of the laser beam.
This is due to the fact that when the insulating substrate is vaporized and removed by the laser beam, the resin portion is removed before the substrate portion.
Next, a tenth aspect of the invention is a method of forming a mounting recess portion by utilizing a technique of forming holes through the irradiation of the laser beam.
That is, the tenth aspect of the invention lies in a method of producing a printed wiring board comprising a mounting recess portion for mounting an electronic part, a conductor pattern, and a heat-sink plate arranged at the bottom of the mounting recess portion, characterized in that a conductor pattern is formed on an insulating substrate;
a heat-sink plate is adhered to a lower face of a portion of the insulating substrate forming the mounting recess portion; and a laser beam is irradiated to an upper face of the portion forming the mounting recess portion to form a mounting recess portion.
The function and effect of the tenth aspect of the invention will be described below.
In the tenth aspect of the invention, as shown in FIG. 56, after the portion of the insulating substrate forming the mounting recess portion is covered with the heat-sink plate, the mounting recess portion is formed by the irradiation of the laser beam. Therefore, an opening portion having a desired size can easily be obtained.
In the tenth aspect of the invention, the laser beam is irradiated toward the portion forming the mounting recess portion to form the mounting recess portion ranging from the surface of the printed wiring board to the heat-sink plate adhered to the opposite side thereof.
In this case, the portion of the insulating substrate forming the mounting recess portion is vaporized and removed by a high energy of the laser beam to successively form a hole toward the inside of the insulating substrate. When the top of the laser beam arrives at the heat-sink plate, the laser beam is reflected on the heat-sink plate. Therefore, the irradiation of the laser beam stops at this time. Thus, there can be formed the mounting recess portion of non-passing type in which one opening portion is covered with the heat-sink plate.
Even when the insulating substrate is thin, the mounting recess portion can be formed without giving damage to the insulating substrate.
Further, the bottom of the mounting recess portion is a surface of the heat-sink plate. Therefore, an electronic part is mounted onto the surface of the heat-sink plate in the inside of the mounting recess portion. As a result, the mounting recess portion having an excellent heat dissipation property can be formed.
Even in case of forming the mounting recess portion passing through a plurality of insulating substrates, it is not required to form a through-hole for the formation of the mounting recess portion every the insulating substrate as in the conventional technique. Furthermore, the positioning of the insulating substrates for connecting the through-holes to each other is useless. Therefore, according to the tenth aspect of the invention, the mounting recess portion can be formed easily and accurately.
It is preferable to be a method of producing a printed wiring board in which the insulating substrate is comprised by laminating two or more insulating layers and a conductor pattern is formed in the inside of the insulating substrate. Thus, a high density wiring of the printed wiring board can be realized.
The thickness of the heat-sink plate is preferable to be 0.01-2 mm. In this case, a high strength is obtained at the bottom of the mounting recess portion and also the working of the heat-sink plate becomes easy. However, when it is less than 0.01 mm, the strength at the bottom of the mounting recess portion becomes low and there may be caused the breakage in the heat-sink plate. While, when it exceeds 2 mm, there is a fear that the working of the heat-sink plate is difficult.
As the laser beam, there are used, for example, a carbon dioxide gas laser, an excimer laser and the like.
As the insulating substrate, use may be made of a synthetic resin alone, a resin substrate of synthetic resin and inorganic filler, a cloth substrate of synthetic resin and inorganic cloth and the like. As the synthetic resin, there are, for example, epoxy resin, phenolic resin, polyimide resin, polybutadiene resin, fluoride resin and so on. The insulating substrate made of only such a synthetic resin may be used as a prepreg or a solder resist to be interposed between the other insulating substrates.
As the inorganic filler added to the synthetic resin, there are glass fibers, silica powder, mica powder, alumina, carbon and the like. The substrate made of a mixture of the synthetic resin and the inorganic filler is higher in the strength as compared with the synthetic resin alone.
And also, the cloth substrate is a substrate made of a cloth woven or knitted in cloth form and a synthetic resin such as glass epoxy substrate, glass polyimide substrate or the like. As such a cloth substrate, there is a substrate obtained by impregnating the cloth with a synthetic resin. As a material of the cloth, there are glass fiber cloth, carbon cloth, aramide cloth and the like. As the synthetic resin, the same material as mentioned above is used.
The conductor pattern means a conductive pattern formed in a plane direction of the insulating substrate such as wiring pattern, pads, lands, terminals and the like. The conductor pattern may be formed by an etching of a metal foil, a metal plating or the like.
The printed wiring board obtained in the tenth aspect of the invention can be used in, for example, memory module, multi-chip module, mother board, daughter board, plastic package or the like.